In order to take full advantage of a spectrum, a modern wireless communication system, such as a Code Division Multiple Address (CDMA), a Wideband Code Division Multiple Address (WCDMA), a Universal Mobile Telecommunication System (UMTS), and a Long Term Evolution (LTE), uses a variable envelope modulation technology which performs amplitude modulation and phase modulation simultaneously. The technology has a high Peak-to-Average Power Ratio (PAPR) and a wide dynamic range. However, a too high PAPR causes a transmitter to have high linearity requirements for a power amplifier and often operate under the level of an envelope peak.
The variable envelope modulation technology needs to use a linear power amplifier to amplify a signal. In order to ensure the linearity and increase the power amplification efficiency, an Envelope Tracking (ET)-based technology is often used. As shown in FIG. 1, a radio frequency signal is input and then transmitted to a radio frequency power amplifier after amplification by a driving amplifier. At the same time, an envelope signal of the radio frequency signal is extracted by an envelope detector, the envelope signal is amplified through a tracking power supply, and the amplified envelope signal is used as a drain voltage of the radio frequency power amplifier. Finally, the amplified radio frequency signal is output through the radio frequency power amplifier.
With the development of the multi-carrier modulation technology, when the tracking power supply performs linear amplification on the extracted envelope signal, the requirements for the bandwidth and efficiency of the tracking power supply are higher. For example, in the process of performing envelope amplification, the bandwidth of an envelope signal may reach tens of MHz, while the bandwidth of a common switching power supply can hardly meet the requirements for the envelope tracking bandwidth due to the limitations of semiconductor technology and switching frequency, and the output noise and distortion may be modulated to a carrier, thus causing out-of-band spectrum spread and severely affecting the Adjacent Channel Power Ratio (ACPR) of the signal. Therefore, a novel fast tracking power supply with high efficiency and high bandwidth is required to meet the growing application needs.